Rooney was in good condition Sunday night, according to a hospital spokesman.

The two boats in the Seadog fleet are among the fastest commercial boats in the nation, traveling at speeds of up to 45 m.p.h. The 70-foot bright yellow and red vessels can carry as many as 149 passengers at a time during 30-minute excursions. There were 30 passengers and two crew members at the time of the accident, police said.

Sunday's was not the first accident that a Seadog boat had been involved in since it began cruising in Chicago two years ago.

Company officials confirmed that a Canadian woman was rushed off the Seadog to an area hospital during a July cruise because her back was injured after the boat sped over a high wave, said Mike Higgins, one of the owners of Seadog Ventures.

And on Oct. 1, the Seadog ran into a moored boat at Navy Pier, causing a gash in the rear of the Spirit of Chicago, but no injuries, according to Higgins.

Witnesses and police said the Seadog boat in Sunday's accident was 60 to 100 feet off the shore when it ran into Rooney.

"It struck me as unusual that the boat would be so close," said Steve Free, 37, of Northbrook, who witnessed the accident. "I've never seen it this close."

A Park District ordinance mandates that boats stay 150 feet outside the shore line and 300 feet away from beaches, Mulligan said.

Rooney and her husband were swimming off the concrete embankment between Oak Street and North Avenue beaches.

Faded painted emblems on the concrete indicate that no swimming is allowed, although residents routinely swim there, Mulligan said. There are no lifeguards on duty after Labor Day.

Police and the U.S. Coast Guard are investigating the accident, Mulligan said.

Higgins said the driver of the boat, William Sutterlin, was traveling about 30 miles per hour when the accident occurred.

Sutterlin apparently did not know he had struck a swimmer.

"He had no idea," Higgins said. "He said that it was the normal cruise route that he takes and that he saw what appeared to be a red balloon in the water. He said he sees balloons out there on a regular basis. It wasn't until he got back to Navy Pier that he learned the situation."

Kelleher noted that about 5 inches of a swimmer's head is visible to boat operators, which is why captains "are always told not to take their eyes off a swimmer once they spot one."

Drew Dillworth, 30, of Chicago, one of two witnesses who rescued Rooney after the accident, said he was responding to her cries for help.

"I was jogging and I heard someone screaming," said a shivering Dillworth. "I ran in and pulled her to shore. Before I touched her, I asked her, `Are you all right?' She said she was, and I grabbed her arm and swam in. She was conscious the whole time."

Paramedics arrived on the scene almost immediately and treated her for shock before she was taken to the hospital.